Monday, November 26, 2007

We report on the results from an ongoing program aimed at testing Newton's law of gravity in the low acceleration regime using globular clusters. It is shown that all clusters studied so far do behave like galaxies, that is, their velocity dispersion profile flattens out at large radii where the acceleration of gravity goes below 1e-8 cm/s/s, instead of following the expected Keplerian fall off. In galaxies this behavior is ascribed to the existence of a dark matter halo. Globular clusters, however, do not contain dark matter, hence this result might indicate that our present understanding of gravity in the weak regime of accelerations is incomplete and somehow incorrect.

Abstract. The competition between CDM and MOND to account forthe ‘missing mass’ phenomena is asymmetric. MOND has clearly demonstrated that a characteristic acceleration a0 underlies the data and understanding what gives rise to a0 is an important task. The reason for MOND’s success may lie in either the details of galaxy formation, or an advance in fundamental physics that reduces to MOND in a suitable limit. CDM has enjoyed great success on large scales. The theory cannot be definitively tested on small scales until galaxy formation has been understood because baryons either are, or possibly have been, dominant in all small-scale objects. MOND’s predictive power is seriously undermined by its isolation from the rest of physics. In view of this isolation, the way forward is probably to treat CDM as an established theory to be used alongside relativity and electromagnetism in efforts to understand the formation and evolution of galaxies.

The cosmic microwave background provides an image of the Universe 0.4 million years after the big bang, when atomic hydrogen formed out of free electrons and protons. One of the primary goals of observational cosmology is to obtain follow-up images of the Universe during the epoch of reionization, hundreds of millions of years later, when cosmic hydrogen was ionized once again by the UV photons emitted from the first galaxies

Under the assumption that general relativity describes the evolution of the Universe, the measured CMB anisotropies indicate conclusively that most of the matter in the Universe must be very weakly coupled to electromagnetism and hence cannot be the matter that we are made of (baryons). This follows from the fact that prior to hydrogen recombination, the cosmic plasma was coupled to the radiation through Thomson scattering. Small-scale fluctuations were then damped in the radiation-baryon fluid by photon diffusion. The damping is apparent in the observed suppression of the CMB anisotropies on angular scales well below a degree on the sky, corresponding to spatial scales much smaller than 200 comoving Mpc. To put this scale in context, the matter that makes up galaxies was assembled from scales of < 2Mpc. In order to preserve the primordial inhomogeneities that seeded the formation of galaxies, it is necessary to have a dominant matter component that does not couple to the radiation fluid

To test empathy levels and the subjects’ reactions to various melodramas, the researchers turned to several classic short stories, like “The Last Leaf” by O. Henry, that include struggles against adversity and melancholy plot twists.

People with low empathy (mostly men) who believed the stories to be fantasies liked them much better than those who were told the stories were factual. The reverse held true for people with high empathy, who were mostly women.

Another surprising observation from the study: not one of the 492 students tested reported having read or heard any of the stories, even though some are quite prominent. “I was appalled,” Professor Argo said.

During several Earth flybys carried out since 1990, some spacecrafts have experienced an unexpected and until now unexplained anomalous velocity increase. This phenomenon is called the flyby anomaly and looks like the effect of an instantaneous acceleration of the spacecraft at the time of closest approach to Earth.

Thursday, November 15, 2007

We discuss the basic difficulties in understanding the origin of the highest energy particles in the Universe - the ultrahigh energy cosmic rays (UHECR). It is difficult to imagine the sources they are accelerated in. Because of the strong attenuation of UHECR on their propagation from the sources to us these sources should be at cosmologically short distance from us but are currently not identified. We also give information of the most recent experimental results including the ones reported at this conference and compare them to models of the UHECR origin.

The highest energy cosmic ray ever detected had the energy of a 290km/h tennis ball! From a single particle. Gasp.

Some of these objects have very extreme dynamical mass to light ratios. Over 100 in some cases.

These very large dynamical mass to blue luminosity ratios naturally lead one to ask whether extremely gas rich dwarf galaxies have abnormally small baryon fractions, i.e. have they just been inefficient at forming stars, or did they end up with less than the typical baryon fraction?

Thursday, November 08, 2007

We now know that neutrinos have masses and that the flavor eigenstates (νelectron, νmuon, νtau ) are not the mass eigenstates (ν1, ν2, ν3).

This means that an electron muon is a quantum mechanical mixture of different masses and a neutrino that has a definite mass is a quantum mechanical mixture of the different flavors (electron, muon, tau).

Tuesday, November 06, 2007

[In talking to an Arab nationalist leader] I said complete independence was what we ultimately wished to give. "My lady" he answered—we were speaking Arabic —"complete independence is never given; it is always taken."

Monday, November 05, 2007

We have constructed a fully functional, fully integrated radio receiver from a single carbon nanotube. The nanotube serves simultaneously as all essential components of a radio: antenna, tunable band-pass filter, amplifier, and demodulator. A direct current voltage source, as supplied by a battery, powers the radio. Using carrier waves in the commercially relevant 40-400 MHz range and both frequency and amplitude modulation techniques, we demonstrate successful music and voice reception.

On the second page of this preprint there's a fascinating image of the center of our galaxy in mid infrared, highlighting GCIRS3, the hottest and most compact of the sources of thermal dust irradiation in that vicinity. It appears that this object is a cool dust-forming carbon star.

Saturday, November 03, 2007

Researchers at the university have bred a strain of "mighty mice," known as PEPCK-Cmus mice because of specific genetic enhancements, that can run for six hours at a speed of 20 meters per minute, or a total of 5 or 6 kilometers.

By fundamental physics, I mean the search for a small set of laws which in principle determine everything we can calculate about the universe. The reductionist dream – not always practical, but very seductive. Where do we stand in the search for these laws? What do we know, and what are the mysteries? Why do many physicists feel stuck?